[coverage] Add coverage delta update handler
[coverage] Add coverage delta update handler

Bug: chromium:1042927
Change-Id: I8af6ad478f613b274ae46e5a6c21aa64b33f39df
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2009110
Reviewed-by: Simon Zünd <38944668e9e2ca98ccd0275b53370f90fa55c113@chromium.org>
Commit-Queue: Sigurd Schneider <f04d242e109628a27a0f75fd49a87722bcf291fd@chromium.org>

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